An approach to modelling the interaction between RANS- and LES-regions of the boundary layer in SST-IDDES simulations

Hybrid RANS/LES methods such as IDDES are an attractive approach to modelling flows with boundary layer separation since they provide a cost-effective alternative to the LES in the whole computational domain and allow us to resolve some of the turbulence. However, these methods still have some drawbacks, viz. unphysical shift in the mean velovity profile within the logarithmic region and an underestimated skin friction coefficient. These drawbacks are attributed to an excessive dissipation of velocity fluctuations at the RANS/LES interface. This work suggests a method of introducing stochastic fluctuations to the interface area. The method eliminates the above hybrid method problems in the case of a zero pressure gradient flat plate boundary layer, where they are apparent, and preserves the solution obtained from the basic IDDES simulation for the curved backstep flow, for which the problems are insignificant. The use of this method allows us to improve the size of the separation bubble.